Dimir Terror's whole plan hinges on Tolarian Terror costing less for each instant/sorcery in the graveyard and Sneaky Snacker (2/1) returning itself from the graveyard once its controller draws a third card in a turn, so a second Relic of Progenitus is excellent, both denying the cost reduction and exiling the graveyard before Sneaky Snacker can boomerang back. Fiery Cannonade's 2 damage kills Sneaky Snacker outright and any small blockers, clearing the way for your bigger threats. Coalition Honor Guard soaks up their limited removal suite (Snuff Out, Agony Warp) on an irrelevant 2/4 body. Cut Barrels of Blasting Jelly, Bojuka Bog, and a Boulderbranch Golem, none of which meaningfully affect this graveyard-dependent matchup as much as the Relics do.